Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$59.27	12.342%	$66.5851	$66.59	$66.60	$66.60
Purchase #2	$193.71	3.634%	$200.7494	$200.75	$200.75	$200.70
Purchase #3	$29.33	7.427%	$31.5083	$31.51	$31.50	$31.50
Purchase #4	$119.97	10.111%	$132.1002	$132.10	$132.10	$132.10
Purchase #5	$199.29	11.680%	$222.5671	$222.57	$222.55	$222.60
Purchase #6	$175.44	11.384%	$195.4121	$195.41	$195.40	$195.40
Purchase #7	$16.76	8.543%	$18.1918	$18.19	$18.20	$18.20
7 purchase totals =	$793.77		$867.1140	$867.12	$867.10	$867.10